BICYCLE WHEEL TRUING STAND

I've made this  project  far more complex that it would need to be.   It was  deliberate.     My son wanted a truing stand, and I thought it would be fun to see how neat we could make it.   Many  commercial  truing stands use sheetmetal pointers or calipers to judge wobble and runout by eye, and they probably work OK.  But when I mentioned to my son that he could get dial indicators that can  indicate thousanths of an inch  for $7.95 each, he liked that idea a lot! 

Click on the thumbnails for enlarged views of the photos. 

First the stand itself.  It's made of 1"square tube, and a piece of 2 x 1/2 x 3/16 channel for the base.  I flycut the top of the base in the mill to make it flat and smooth, and milled a slot in it.    One arm can slide back and forth to accomodate different axel widths.  There are tee nuts underneath that the Allen screws engage.  These run in the slot, with about .002" tolerance so the arm is always aligned.  After making it we zinc-plated the stand and the teenuts for appearance and so they won't rust.   Paint would scrape off the sliding parts, but zinc will hold up OK.   Zinc plating is almost as easy as painting and it's fun.

The parts were too long to fit in my 2-gallon zinc bucket but no problem.   We bought a long narrow plastic tub for two bux from a nursery.  I think they use these vessels for lining planters.   Zinc "throws" well so it worked as you can see.   

The runout dial indicator mount uses two locks.  The lock for the cross rod is a "cotter", like the quill lock on a Bridgeport mill.     There are two perpendicular holes that partially intersect.  The cross rod goes thru the horizontal hole.  It  has a right-angle bend in it and a DI mounted on its other end.  As it rotates in the horizontal hole,  the rod will "nod" up and down for adjusting the position of the DI relative to the wheel.  In the vertical hole  are two short pieces of  .375" dia brass rod that had a cylindrical recess cut in it perpendicular to its axis with a 3/8" end mill.   Then they were parted in the middle of this semicircular notch.     One is threaded 10-32.  The locking screw goes thru  one of these and screws into the other.    When the screw is rotated,  the brass slugs pinch the crossrod and lock it up.   There is a semicircular groove in the cross rod that clears the screw, so when the screw is in place the cross rod is captive.      Locking  action is very crisp;  less than 1/4 turn from dead loose to locked tight.      This is the final assembly after nickel plating.  I used  nickel here because it resists skin acids better than zinc, and because the part was small enough for my setup. 

This is an exploded view of the cotter.   There's  a 5/16" - 18 hole in the bottom. A bolt with washer comes up from the bottom and tightens against the sqare tang on the bottom of the body.   This tang was intended to be the full width of the body but -- I accurately made  it oriented 90 degrees away from where it was supposed to be.       Oops.    The square peg is what's left, and it  works well enough.  This tang and the tangs on the ring  to the right of it engage the slot in the base.  When the bolt and washer are snug up against the square tang,  the assembly is still free to slide back and forth.  Before mounting, the  threaded collar is screwed onto the body as far as it'll go.  Then the ring with tangs is added to the stack and the lot assembled to the base with the bolt and washer.    The threaded collar is only threaded for about 3 threads, and then its ID is reduced to a couple of thou larger than the body diameter for about 0.1" of length.  This conceals the threads.      In operation,  when the threaded collar is rotated clockwise with the lower lever,    it jacks the body up away from the thrust ring  until the washer beneath jams against the frame and the assembly locks in place.   The threads are .870 - 24, lathe-cut on both body and collar.   Operation of this mechanism is also very crisp and smooth; less than 1/8 of a turn of the locking collar takes it from free-sliding to locked down snug.  

The runout DI mounting arm that rides in the cotter needed   a right-angle bend in it.  Could just bend the rod, right?   Naahhh, that's no fun!  I thought it would look cool if the joint was made with a ball.  So that's how I made it.  

I wanted to use  my procedure for making balls on a mill with an indexing head anyway.  An article  describing this  procedure will appear in Guy Lautard's next book.   That's how this  ball was made.

Then I milled orthogonal flats on the ball, drilled and reamed .250 dia x .100 deep pilot holes.  These accept mating pegs turned on the ends of the shafts, to keep the shafts  located  while  silverbrazing. 

The shaft looks like this.  It's zinc-plated.     The little threaded peg is 1/4-28 to fit the tang on the back of the DI.      I could have just drilled and tapped the DI mount 1/4- 28 rather than brazing in a peg, but this way the locking mechanism is  invisible when the parts are      assembled. 

Here's how the DI is mounted to the end of the arm.  There's a D-shaped washer between the locknut and the DI; the flat on the D rides the flat on the mount.  It  seems to make quite a difference.  The knurled knob is only 0.5" dia but only modest fingerforce is necessary to secure it.  The knob and the D-washer are nickle-plated.   Cold-blueing  or black oxide  could have worked too.  A good machined finish does not rust quickly and a polished finish resists rust surprisingly well  -- but a knurl rusts right now if not protected one way or another.  

Here it is assembled with the runout DI in place.  The white thing on the DI is a little "flatfoot" machined out of delryn to provide a good tracking surface on the rim,  eliminate any possiblity of marring or scarring the wheel, reduce friction and make it quiet.   Friction is low enough that this lightweight aluminum wheel will spin a couple of turns under it's own momentum with the DI riding the rim.  

 While checking it out yesterday we discovered that MSC has a nice "switchable" magnetic base DI stand, with DI, on sale for $19.99.   That wouldn't have worked well for the runout DI because of wheel clearance, but it'll work great for the wobble DI.  It'll go on the left end of the base, just need a couple of arms.    Kevin's gonna order one today.   

4-01-02